title: A density functional study of the adsorption of methane-thiol on the (111) surfaces of the Ni-group metals: I. Molecular and dissociative adsorption.
abstract: The molecular and dissociative adsorption of methane-thiol (CH(3)SH) in the high-coverage limit on the (111) surfaces of the Ni-group metals has been investigated using ab initio density functional techniques. In molecular form, methane-thiol is bound to the surface only by weak polarization-induced forces in a slightly asymmetric configuration with the C-S axis tilted by 35-60° relative to the surface normal. On Ni and Pd surfaces the S atom occupies a position close to a bridge site; on Pt it is located close to an on-top position. The length of the S-H bond is only slightly stretched relative to its value in the gas phase, indicating only a very modest degree of activation for dehydrogenation. A strong covalent adsorbate/substrate bond is formed upon adsorption of a methane-thiolate (CH(3)S) radical. On Ni(111) in the energetically most favorable configuration the S atom occupies a position in a threefold hollow, slightly displaced towards a bridge site. The C-S axis is tilted by about 35° across the bridge. On Pd(111) and Pt(111) the S atom of thiolate occupies a position between a hollow and a bridge site, with the C-S axis tilted even more strongly across a neighboring threefold hollow. On all three surfaces our calculations demonstrate the existence of multiple metastable adsorption configurations, including upright CH(3)S bound in the center of a threefold hollow as reported in some earlier studies. Dehydrogenation of the adsorbed methane-thiol to form co-adsorbed methane-thiolate and atomic hydrogen is an exothermic process, which is not activated on Ni(111) but activated on Pd(111) and Pt(111).
authors.affiliation: Fakultät für Physik and Center for Computational Materials Science, Universität Wien, Sensengasse 8/12, A-1090 Wien, Austria.
authors.forename: David
authors.initials: D
authors.lastname: Karhánek
authors.forename: Tomáš
authors.initials: T
authors.lastname: Bučko
authors.forename: Jürgen
authors.initials: J
authors.lastname: Hafner
mesh_terms: D000327:Adsorption; D002244:Carbon / Q000737:chemistry; D003198:Computer Simulation; D005609:Free Radicals / Q000737:chemistry*; D006859:Hydrogen / Q000737:chemistry; D008670:Metals / Q000737:chemistry*; D008956:Models, Chemical; D009532:Nickel / Q000737:chemistry*; D010165:Palladium / Q000737:chemistry; D010984:Platinum / Q000737:chemistry; D011789:Quantum Theory; D013438:Sulfhydryl Compounds / Q000737:chemistry*; D013455:Sulfur / Q000737:chemistry*; D013499:Surface Properties
chemical_list: D005609:Free Radicals; D008670:Metals; D013438:Sulfhydryl Compounds; C005231:methylmercaptan; D010984:Platinum; D010165:Palladium; D013455:Sulfur; D002244:Carbon; D009532:Nickel; D006859:Hydrogen